Sometimes, just once or twice in a lifetime, something beautiful and strange and infinitely poignant comes along: something that causes you to put down your drink and blow a thin stream of air out between your lips and give a small inward prayer of thanks for the simple fact of being alive in the world right now.

Such a thing is the news that four former cast members of the 1970s TV show Happy Days, and the widow of another, are suing CBS for $10m (£6m) in unpaid merchandising revenue.

From every angle you inspect this story, it brings more joy – and not only because it causes you to spend at least eight hours straight singing "Monday, Tuesday, HAPPY DAYS! Wednesday, Thursday, HAPPY DAYS!, Friday, Saturday, HAPPY DAYS!" until your significant other hits you with a pan.

The five plaintiffs are Marion Ross (who played Marion Cunningham), Anson Williams (Potsie), Don Most (Ralph Malph), Erin Moran (Joanie), and the widow of Tom Bosley, who played Howard Cunningham. Absent from the suit – presumably on the grounds that they are doing very nicely thank you, and could do without being subjected to wide public mockery and/or being reminded they used to be in Happy Days – are Ron Howard and Henry Winkler, aka Richie and the Fonz.

The actors' contracts had it that they were due between 2.5% and 5% of merchandising revenues, and they say they've never seen a dime. The first thing you may think is: what merchandise? This was the 70s, after all: the days before things were all about the merch. OK, Star Wars was all about the merch. But Happy Days?

Well, that's what I thought – but it's there. On eBay and similar you can find enamel badges that ask, "What Would the Fonz Do?", T-shirts and jacket patches, playing cards and stickers. No doubt if you drill a little deeper, you will find novelty doorbells that go "Cunning-HAM!", keyrings with dangling plastic replicas of That Shark, and Happy Days pinball machines in which "TEABAG!!" lights up and you get a free ball if you land one in Chachi's mouth.

But here's the thing: everything you can imagine being merchandisable about this show was to do with the Fonz; or, if bowling shoes and slightly nerdy baseball caps are your thing, at a pinch Richie Cunningham.

Happy Days, as all who loved it will well remember, opened a weird window in the space-time continuum, being an insanely 1970s imagining of a 1950s that never happened. This lawsuit opens a window into something even stranger: a world in which the images of Howard, Marion, Potsie, Joanie and Ralph Malph shifted so much merchandise that 5% of it adds up to £6m. That is to suggest that (surreptitiously consults calculator) people bought between £120m and £240m of novelty gewgaws, trinkets, DVDs, slot machines, drinks coasters etc with Potsie on them. Can anyone now, honesty, even remember what Potsie looked like?

Where are these drinks coasters and novelty playing cards? Why are they not turning up on Cash in the Attic? You'd think if £240m of Ralph Malph frightwigs were extant in the world, we'd have noticed them. More to the point, you'd think Ralph Malph would have noticed them.

Yet, oddly – and infinitely touchingly, to my mind – the principals seemed oblivious to this frenzy of marketing. In 2002, according to one report, Moran rang the studio and asked if there was any merchandising money owed, was told there wasn't any, and went (un)merrily on her way.

Ross only tumbled to her enduring celebrity in the merchandising world when a stranger tipped her off. "The other day someone came up to me and said, 'You must be cleaning up on those casinos,'" she said. "And I said, 'Well, what are you talking about?' And he said, 'If you get five Marions, you get the jackpot.'"

It's too soon to know what the outcome of the lawsuit will be. Negotiations seem to have stalled over the difference between the $10m the actors say they are owed and the $9,000-ish that CBS thinks they are owed. We can say, however, that it looks like a PR disaster for the network.

I can't be alone in finding it impossible to separate the actors from their bizarrely wholesome 1970s/1950s personas on the show; which means that, for me, it's not Marion Ross fighting through court for her unpaid slot machine revenues, it's Marion Cunningham. Who won't be rooting for her to win a five-Marion jackpot?